Dual feed antenna



y 2, 1961 c. c. JONES 2,982,961

DUAL FEED ANTENNA Filed March 20, 1957 IN V EN TOR.

c/mv/ a. (/0 E6 BY W 7% E5 .4. Z

DUAL FEED ANTENNA Calvin C. Jones, Jessup, Md., assignor, by mesneassignments, to the United States of America as represented by theSecretary of the Air Force Filed Mar. 20, 1957, Ser. No. 647,457

2 Claims. (Cl. 343-840) This invention relates to a dual feed antennasystem I wherein a radar antenna system which radiates and receiveshorizontally polarized energy is modified by adding an IdentificationFriend or Foe feed which radiates and receives vertically polarizedenergy. The Identification Friend or Foe feed shall hereafter bereferred to as the identification feed.

The object of the invention is to provide an identification feed systemat the focal point of a radar reflector with parasitic reflectors, forthe identification dipole elements, that do not affect the operation ofthe radar system.

This and other objects are accomplished by providing vertical slats asthe parasitic reflecting elements, which intercept the verticallypolarized identification energy but do not aifect the horizontallypolarized radar energy.

In the drawing,

Fig. 1 is a side view of the dual feed system together with the modifiedreflector.

Fig. 2 is a front view of the modified reflector.

Fig. 3 is a side view showing the radar feedhorn and the identificationfeed.

Fig. 4 is a top view of the radar feedhorn with the identification feedattached thereto.

Referring more particularly to Fig. 1, reference numeral 10 refers to aradar reflectorhaving a parabolic section 11, a barrel section 12 and aplurality of horizontal slats 13 for reflecting horizontally polarizedradar energy. The reflector was modified to reflect vertically polarizedidentification energy by adding a plurality of vertical slats 14.

Beam shaping antennas having a parabolic section and a barrel sectionare well known in the art. One such antenna is shown in Figs. 13-17 onpage 484 of volume 12 of the MIT Radiation Laboratory Series.

The antenna system has a radar feedhorn 15 and an identification feedsystem 16 located at the focal point of the reflector 10, with theidentification feed attached to the feedhorn 15.

An identification feed consisting of two dipoles with metal plates forparasitic reflectors was first tried. Since the focal point of thereturn energy from the barrel section is also the focal point for theparabolic section, an energy field of high intensity results in thisregion. The metal plates intercepted a considerable amount of the radarbeam'energy. This eflfect was eliminated in a man- United States Patent2,982,961 Patented May 2, 1961 ner which will be explained withreference to Figs. 3 and 4.

In Figs 3 and 4, the reflecting elements 17 and 18 for dipoles 19 and 20consist of a plurality of vertical slats 21 and 22, respectively. Whenvertical slats are substituted for the reflecting plates, they interceptthe vertically polarized identification energy, but do not intercept thehorizontally polarized radar energy. The identification feed is attachedto the radar feedhorn by means of plates 23 and 24.

There is thus provided a dual feed system wherein the detrimental efiectof the dipole parasitic reflectors is greatly reduced, if not eliminatedentirely.

While a certain embodiment of the invention has been described in somedetail, it will be understood that numerous changes may be made withoutdeparting from the general principles and scope of the invention.

What is claimed is:

1. An antenna system comprising reflecting means for reflecting energyin two planes of polarization which are displaced 90 from each other,said reflecting means having a focal point, a radar feedhorn located atsaid focal point for receiving and radiating energy in one of saidplanes of polarization, an identification feed located at said focalpoint and mounted on the external surface of said said radar feedhornfor receiving and radiating energy in the other of said planes ofpolarization, said identification feed comprising two dipole elementsand two parasitic reflectors, each of said dipole elements beingadjacent to and carried by one of said parasitic reflectors, saidparasitic reflectors being mounted on opposite sides of said radarfeedhorn, each of said parasitic reflectors consisting of a plurality ofparallel slats for directing energy from said dipole elements towardsaid reflecting means.

2. The system of claim 1, wherein said radar feedhorn receives andradiates energy in a horizontal plane of polarization and saidedntification feed receives and radiates energy in a vertical plane ofpolarization.

References Cited in the file of this patent UNITED STATES PATENTS2,216,707 George Oct. 1, 1940 2,398,096 Katzin Apr. 9, 1946 2,430,568Hershberger Nov. 11, 1947 2,441,574 Jaynes May 18, 1948 2,669,658Jackson Feb. 16, 1954 2,691,731 Miller Oct. 12, 1954 2,753,551 RichmondJuly 3, 1956 2,820,965 Sichak Jan. 21, 1958 FOREIGN PATENTS 399,770Great Britain Oct. 12, 1933 409,116 Italy Feb. 1, 1945 OTHER REFERENCESMIT Radiation Laboratory Series, vol 12, Microwave Antenna Theory andDesign, by Silver, 1949.

